The present invention relates to a propulsion system for a craft, the system comprising two jet engines, which are arranged parallel to one another, and an inlet and/or outlet device for each jet engine, each device comprising a duct for carrying a gas, the duct having a gas inlet and a gas outlet. The invention further relates to an aircraft comprising the propulsion system and to an outlet device for a jet engine.
The term jet engine is intended to include various types of engines which take in air at a relatively low velocity, heat it up through combustion and expel it at a much higher velocity. The term jet engine includes turbojet engines and turbofan engines, for example.
The jet engine conventionally comprises a compressor section for compression of the intake air, a combustion chamber for combustion of the compressed air and a turbine section arranged behind the combustion chamber, the turbine section being rotationally connected to the compressor section in order to drive this by means of the energy-rich gas from the combustion chamber. The compressor section usually comprises a low-pressure compressor and a high-pressure compressor. The turbine section usually comprises a low-pressure turbine and a high-pressure turbine. The high-pressure compressor is rotationally locked to the high-pressure turbine via a first shaft and the low-pressure compressor is rotationally locked to the low-pressure turbine via a second shaft. The jet engine can be used for the propulsion of various types of jet-propelled craft including both land and waterborne craft, but the invention is primarily intended for applications in an aircraft, and in particular in an airplane engine.
Protecting an airplane against possible attack by giving the airplane a low so-called signature is already known. The term signature in this context refers to the contrast with the background. A craft should have a low signature in respect of such things as radar waves and infrared radiation. For example, hot structures and hot exhaust gases give rise to an IR signature. The scope of the invention consequently includes systems which provide passive countermeasures against infrared detection and/or radar detection.
It is desirable to provide a propulsion system for a craft, which will give the craft a reduced signature in operation.
A propulsion system for a craft, the system comprising two jet engines, which are arranged parallel to one another, and an inlet and/or outlet device for each jet engine, each device comprising a duct for carrying a gas, the duct having a gas inlet and a gas outlet, characterized in that the gas outlet is arranged offset in relation to the gas inlet transversely to the longitudinal direction of the duct, so that the jet engine is hidden from external view.
The gas duct between the gas inlet and the gas outlet therefore has a curved shape. The fact that radar waves have to bounce several times against the duct walls on their way in towards the jet engine affords a reduced signature in respect of radar detection. The surface may be provided, for example, with radar absorbing materials, thereby achieving a low radar target area.
According to a preferred embodiment of the invention the gas ducts along one section are convoluted around one another. In this way a space-efficient propulsion system is achieved. The two gas ducts accordingly cross one another viewed at right-angles to a plane in which the central axes of the jet engines extend.
The above applies both to an inlet device, that is to say a device arranged upstream of the jet engine, and to an outlet device, that is to say a device arranged downstream of the jet engine.
Where the outlet device has the aforementioned design configuration, internal hot/reflective parts of the engine are hidden from rear view. Hot parts of the jet engine, such as a rear turbine rotor are therefore visually masked from rear view. This substantially reduces the IR signature.
The invention will be described below for a propulsion system in respect of the configuration of the outlet devices for two jet engines. It will be appreciated, however, that the invention can also be implemented for a corresponding inlet configuration.
It is also desirable to provide an outlet device for a jet engine, which will give the jet engine a reduced signature.
An outlet device according to an aspect of the present invention comprises a duct for carrying a gas, the duct having a gas inlet and a gas outlet. The gas outlet is arranged offset in relation to the gas inlet transversely to the longitudinal direction of the duct, so that the gas inlet is hidden when viewed from the outlet side. When the outlet device is installed behind the jet engine, the internal hot/reflective parts of the engine will be hidden from rear view. Hot parts of the jet engine, such as a rear turbine rotor are therefore visually masked from rear view. This substantially reduces the IR signature.
Further preferred embodiments and advantages of these are set forth in the following description, in the drawings.